This invention relates to a magnetic element and a magnetic-element array. More particularly, the invention relates to a magnetic element in which a recording of a direct-current-driving type and a reproduction by the magnetoresistance effect are possible, and a magnetic element array.
Since the discovery that giant magnetoresistance effect (MR) is exhibited when a current is supplied to flow in parallel with the major plane of a multi-layered structure, efforts have been paid to find systems having still larger magnetoresistance ratios. Heretofore, ferromagnetic tunnel junction elements and CPP (current-perpendicular-to-plane) type MR elements in which electric current flows vertically in a multi-layered structure have been developed and regarded hopeful as magnetic sensors and reproducing elements of for magnetic recording.
Recently, “magnetic nanocontacts” by tip-to-tip abutment of two nickel (Ni) needles and nanocontacts by contact of two magnetite elements were reported as elements exhibiting 100% or higher magnetoresistance effects in the literatures, (1) N. Garcia, M. Munoz and Y. W. Zhao, Physical Review Letters, vol. 82, p 2923 (1999) and (2) J. J. Versluijs, M. A. Bari and J. M. D. Coey, Physical Review Letters, vol. 87, p 26601-1 (2001), respectively.
These nanocontacts certainly exhibit large magnetoresistance changes. In both proposals, however, the magnetic nanocontacts are made by bringing two needle-shaped or triangular-section-shaped ferromagnetic elements into tip-to-tip contact. Furthermore, it is as a system which shows the bigger magnetoresistance effect.
These magnetoresistance effect elements can be used not only as a reproduction element of a magnetic sensor or a magnetic record reproduction system, but also as an element of a non-volatile magnetic memory.
When the magnetoresistance effect element is used as a magnetic element, therefore, writing is carried out by a leak current magnetic field applied from a wiring provided near the magnetoresistance effect element.
However, there is a problem that current required to cause the magnetization reversal for recording is as large as several micro amperes or more.
On the other hand, as a new mechanism of a magnetization reversal, a magnetization reversal of a “direct-current-driving” type has been found, where the magnetization reversal for recording can be carried out by flowing a current directly to the recording magnetic part of the element (J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996), E. B. Myers, et al., Science 285, 867 (1999), J. A. Katine, et al., Phys. Rev. Lett., 14, 3149 (2000), F. J. Albert, et al., Appl. Phy. Lett., 77, 3809 (2000), J. E. Wegrowe, et al., Europhys. Lett., 45, 626 (1999), J. Z. Sun, J. Magn. Magn. Mater., 202, 157 (1999))
In this mechanism, when a writing current is passed through a magnetic reference part or a surrounding magnetic layer, the spin of the current is polarized. When this spin-polarized passes through the magnetic recording part, magnetization of the recording magnetic part is reversed by transmitting the anglar momentum of the spin-polarized electron to the anglar momentum of the magnetic recording part. By using this mechanism, it is expected that current required for magnetization reversal for writing decreases, since it is possible to make the writing action more directly to the recording layer.
So far, such a magnetic element of direct-current-driving type has been a device that is discrete and different from the magnetoresistance effect element. The inventors have first conceived that by combining these different elements, a novel and convenient magnetic element could be realized, by which both recording and reproducing can be performed while reducing the element size.
However, since resistance of the recording part including the magnetic recording part is very small, it is difficult to simply combine such a direct-current-driving type magnetic element with a conventional magnetoresistance effect element which may have a far larger resistance. Besides, since resistance of the recording part is very small, a selection of a specific element in an element array becomes especially difficult.
As explained above, although a reduction in the writing current is expected with a magnetic element using the direct-current-driving magnetization reversal, there is a problem that it is difficult to make element selection when the elements are integrate in an array configuration.